This invention relates to a conveyor belt useful for supporting and conveying glass substrates through a curing furnace.
Touch screens are now ubiquitous and used as the input and display interface at, for example, automatic teller machines, gambling machines in casinos, cash registers, and the like. Touch screen panels generally comprise an insulative (e.g., glass) substrate and a resistive layer disposed on the insulative substrate. A pattern of conductive edge electrodes are then formed on the edges of the resistive layer. The conductive electrodes form orthogonal electric fields in the X and Y directions across the resistive layer. Contact of a finger or stylus on the active area of the panel then causes the generation of a signal that is representative of the X and Y coordinates of the location of the finger or stylus with respect to the substrate. In this way, the associated touch panel circuitry connected to the touch panel by wiring traces can ascertain where the touch panel occurred on the substrate.
Typically, a computer program generates an option to the user (e.g., xe2x80x9cpress here for xe2x80x98yesxe2x80x99 and press here for xe2x80x98noxe2x80x99xe2x80x9d) on a monitor underneath the touch screen panel and the conductive electrode pattern assists in detecting which option was chosen when the touch panel was touched by the user.
During the production of a touch screen panel, the panel may be subjected to one or more manufacturing steps wherein it is placed in or conveyed through an oven or furnace. High temperature curing is also a common processing step in the manufacture of many products using glass substrates (e.g., touch screens, flat panel displays, etc.) The glass substrate and/or fragile coatings on one or both surfaces of the substrate can be damaged by physical contact. Prior art methods of transporting glass substrates through conveyor furnaces commonly use metallic conveyor belts. The glass substrates are placed directly on top of and in full contact with the metal conveyor belt. This causes several problems. First, both glass substrates and coated glass substrates have fragile surfaces that are easily scratched by contact with the hard metal conveyor belt surface. Second, metal conveyor belts have large thermal mass and have different thermal properties than glass. When glass substrates are in contact with a large area of the metal conveyor belt, glass breakage in heating and cooling is a major process yield issue. This is even worse in a rapid thermal process where the glass substrates are heated and cooled as quickly as possible. Third, the standard conveyor belt does little to position or guide the substrate while it travels through the furnace nor does it provide a predictable position at the exit end of the furnace so that the substrate can be correctly fed to downstream processes.
Sometimes, high-temperature fabrics are used as insulation between the standard metal conveyor belt and the glass substrates to control glass breakage and scratching. The problems with this method are that many uncured coatings can not be placed in direct contact with the fabric without being damaged. Also, the fabric materials often liberate fibers which can contaminate the product. In addition, the fabric pads have to be individually placed on the belt under the substrate and thus are conducive only to a manual, non-automated operations.
In some cases, metal trays or xe2x80x9cboatsxe2x80x9d are used to transport glass substrates on standard metal conveyor belts. These trays allow the glass substrate to be supported by the edges and elevated off of the conveyor belt. Problems with these trays include glass breakage due to the significant thermal mass and different heating and cooling rates than the glass they support. Also, they must be individually placed on the conveyor belt and under the glass substrate making them appropriate only for manual, non-automated processes. Finally, the trays are somewhat fragile and require maintenance, cleaning and replacement on a regular basis.
Driven ceramic rollers can also be used to transport glass substrates through a process furnace. The rollers can be made so that they contact the glass only on two edges and provide minimal frictional contact. Problems with this method include the necessity for a complicated drive train required to synchronously drive all the rollers in the furnace. Second, the rollers are mounted in fixed positions in the furnace. In operation, each roller will achieve a steady-state temperature depending on its position in the heating or cooling section of the furnace. As a substrate is conveyed through the furnace, it gains and rejects heat at a rate dependent on its material properties and mass. When the glass substrate contacts a significant area of a ceramic roller that is not close to its surface temperature, glass breakage can occur. This is especially true for rapid thermal processing. Third, ceramic roller contact with the glass can cause abrasion that can contaminate the product with glass particles, ceramic particles, or both.
Edge conveyors can also be used to support and transport glass substrates through a conveyor furnace. Parallel edge conveyors can be designed to be adjusted in an automated manner and provide a predictable positioning of the substrate inside the furnace and as it exits the furnace to feed downstream processes. Some problems with edge conveyors are the fact that they are complicated and expensive devices that incorporate special components that are designed to survive in a high-temperature environment. Sometimes, special liquid cooling systems are required to maintain component temperatures within acceptable limits. In addition, edge conveyors take up substantial space in the furnace and require the furnace chamber to be made larger than normal to accommodate them. Edge conveyors also have substantial thermal mass and require that the furnace power be greater than normal to accommodate them. Operating costs are then greater than normal. Finally, adjustment of the edge conveyor system must be made either manually or through a control signal actuating a drive component.
It is therefore an object of this invention to provide a new conveyor belt for supporting and conveying glass substrates and other fragile or delicate items through a conveyor furnace.
It is a further object of this invention to provide such a conveyor belt which prevents scratching of the item placed thereon.
It is a further object of this invention to provide such a conveyor belt which avoids breakage of the item placed on it and which overcomes the thermal mismatch problem associated with prior art conveyor belts.
It is a further object of this invention to provide such a conveyor belt which automatically guides the items placed thereon into the correct position.
It is a further object of this invention to provide such a conveyor belt which is better suited to automated manufacturing processes.
It is a further object of this invention to provide such a conveyor belt which is simple in design and which can be manufactured at a low cost.
It is a further object of this invention to provide such a conveyor belt which eliminates the need for high-temperature fabrics and the problems associated with them including contamination.
It is a further object of this invention to provide such a conveyor belt which eliminates the need for metal trays and the problems associated with them.
It is a further object of this invention to provide such a conveyor belt which overcomes the problems associated with driven ceramic rollers and edge conveyors.
The invention results from the realization that the problems associated with prior art conveyor belts used to transport sensitive or fragile items such as touch screens through a furnace or oven, namely the formation of scratches, contamination, and breakage due to thermal mismatching can be overcome by bending certain flight members of a conventional wire belt upwardly to define elevated and inclined support surfaces which only contact the edge of the glass touch screen at one small point and support the touch screen above the belt to better guide touch screens of different sizes without scratching, breaking, or contaminating them in an automated fashion.
This invention features a conveyor belt comprising a series of predefined sections and elevated support structures at the edges of each end of each section for supporting items on the belt above the belt at each said section. Typically, each support structure is sloped outwardly upward and each section includes a plurality of flight members. The support structure is typically formed by bending a set of the flight members upwardly to define an elevated surface inclined outwardly upward. The preferable angle of incline is between 5xc2x0 and 10xc2x0. The elevated support surface can be elevated from between 0.2 and 0.4 inches from the belt at its lowest point and from between 0.5 and 0.7 inches from the belt at its highest point and each elevated surface has a typical length of between 1 and 2 inches to accommodate items of different size.
Usually, the bent set of flights are spaced from each other and there are a number of bent flights at the edges of each section. Also, each section usually includes more than one product travel lane. In the preferred embodiment, the elevated support structures are integral with the conveyor belt.
A method of manufacturing a touch screen in accordance with this invention includes bending selected flight members of a conveyor belt in an oven upwardly to define a plurality of elevated surface each inclined outwardly upward at the end of selected sections of the belt and placing the touch screens on the belt such that the edges of the touch screen rest on the elevated surfaces to dry, cure, or fire the touch screen in an oven without the touch screen touching the conveyor belt other than at the edges. One conveyor belt according to this invention includes a series of predefined sections each including a plurality of flight members, a set of flight members at the edges of each section bent upwardly to define elevated and inclined support surfaces.